This is an excellent introduction to the vertex form of a quadratic function.

http://www.heymath.com/main/samples/us21/teacherstemplate.html

This web page isn't particularly interactive, but it is an excellent application of quadratic functions.

http://www.heymath.com/main/samples/us20/teacherstemplate.html

A flipchart on the vertex form of a quadratic function and its graph.

A TI-Nspire Activity. In this activity, students will explore quadratic functions in the form of a motorcycle jumping off of a ramp. Students will maximize the height of the jump and the airtime of the jump.
http://www.tialgebra.com/activities/algebra_ii/337/